The main factors to win the game are to control the board and your health. There are a lot of different ways to combine those factors. You can defense during the game and then summon powerful Legendaries and destroy your opponent. But the most popular way is to summon creatures with unique bonus effect, play on curve, deal perfect trades and consolidate your advantage on the board. This is the main characteristics of midrange decks that are the most popular nowadays.
The curve of your deck should be uniform. Midrange deck must have some 0 or 1 drops, good 2 drops, some cards for late game from 6 to 8 magicka cost cards (sometimes we can use strong Legendaries that cost 9 or more magicka), and mostly 3,4 and 5 drops (especially cards that costs 4 magicka). If you build Midrange decks you will pay attention to chances of combine summon bonus effects of cards, to use a lot of keywords and to deal trades and control the board but will not forget about your health.
You can use almost of keywords when you play midrange decks. There must be at least 12 percent of cards with Prophecy. They helps you to come back on the board or to increase your advantage. Keyword Drain (maybe it will be keyword Heal) will help you to restore your health if you play against aggro decks. There is a good synergy between creatures with keywords Ward and Pilfer and you can use it in your decks. Sometimes it is very important to play creatures with keyword Guard in midrange decks and there are some of them that have keyword Prophecy too. You can also use cards with all other keywords except Regenerate.
The cards with Agility Attribute are perfect to play them in Midrange decks. You can control the board with destroying Wounded enemy creatures, you can trigger your Last Gasp and Pilfer effects after playing
There is a synergy between cards with keywords Last Gasp like
You can play Midrange decks with Endurance Attribute because of good unique creatures for mid game like
We can use strong five and four-drops with Strength Attribute like
In Midrange decks Willpower Attribute is very important to create especially Token decks. It means that you can play a lot of creatures and give them all buffs(two Ongoing effects by
This is an example of the Midrange crusader deck:
So it is very interesting to play midrange decks because of a lot of different combos during the game and using different keywords to have a win condition.